Dewaxing of petroleum oils



Reissued Sept. 4, 1934 UNITED STATES PATENT OFFICE DEWAXING OF PETROLEUMOILS Nu Drawing. Original No. 1,881,643, dated October 11, 1932, SerialNo. 147,383, November 9, 1926. Application for reissue April 15, 1933,

Serial No. 666,323

29 Claims.

This invention relates to a method of refining petroleum by removingwax, and certain impurities in some instances, from the petroleum in itscrude state or from petroleum distillates or residues, or mixturesthereof, and thereby producing wax-free oil for any purpose, andparticularly to a method of obtaining substantially wax-free oil andwax, as separate products from wax containing lubricating oil stocks.

In the production of lubricating oil it is desirable to remove from thelubricating oil stock enough of the wax, that was brought into orremains in such stock as a result of the production of such stock fromwax-containing crude petroleum, to cause the final product to have asuitable cold test. The character of the wax in lubricating oil stockvaries according to the process by which the stock was produced andvaries according to the source of the crude petroleum from which thestock was produced. The wax in lubricating stock may substantially allbe crystalline or it may substantially all be amorphous, or the wax mayconsist of both crystalline and amorphous waxes present in differentproportions. The wax in heavier residues of steam distillation and inthe heavier distillates of such distillation is amorphous and the wax inlighter distillates of steam distillation and in most distillates and.in some residues obtained by fire distillation is crystalline. Inintermediate distillates of both fire and steam distillation amorphouscharacteristics of the wax may predominate. If a distillate or residuecontains wax having predominating amorphous characteristics that wax maybe changed to crystalline wax by subjecting the oil to fire or crackingdistillation but in such an operation a considerable quantity of morevaluable oil is lost and gas oil of lower value is necessarily produced.Obviously similar conditions regarding the wax content exist in stocksobtained from petroleum and used for the production of oils for otherpurposes such as medicinal use and insulation and immersion ofelectrical apparatus; and it is well known that crude petroleum containsboth crystalline and amorphous wax in proportions depending upon itssource.

In older practice petroleum oil containing wax that is crystalline hasbeen freed of that wax to a more or less desirable extent by chillingand filter pressing the petroleum oil, and certain oil stocks, such ascylinder stocks, that contain amorphous wax have been freed of that waxto a limited extent, producing oil having a cold test unacceptable inthe light of present standards, by diluting the oil and then chillingthe solution thereof and allowing the chilled solution to settle bygravity. In such gravity settling some wax of crystalline nature issometimes added to assist the settling operation.

In later practice wax has been separated from lubricating oil stock bydiluting the waxcontaining oil and chilling the mixture and thenseparating the wax from the chilled mixture by centrifugal processesdescribed in the patents of Philip T. Sharples No. 1,416,890, No.1,416,891, No. 1,232,104 and No. 1,351,265. The processes of thoseSharples patents are entirely operative and have gone into extensivecommercial use but in cases where the wax in the lubricating oil stockis all crystalline in nature it cannot be separated from the lubricatingoil stock by those processes. For example, those processes will noteffect separation of wax from the heavy fractions produced by fire orcracking distillation of crude petroleum from Pennsylvania.

I have discovered that if a body of oil, such as crude petroleum ordistillates or residues thereof or stocks derived from petroleum for theproduction of oils for special uses, contains wax that is so largelycrystalline in nature that it cannot be separated from the oil to adesired degree by known centrifugal processes, oil having a suitablecold test, and therefore free of wax to a desirable degree can beproduced by centrifugal processes from such crystalline-wax-containingoil, provided the condition of the mixture of petroleum oil and wax isso regulated that the wax, upon being precipitated by chilling, is in astate in which it may be removed from the oil by centrifugal separation,e. g., in a state in which the precipitated wax is of greater averagespecific gravity than crystalline wax and is sufficiently plastic oramorphous to pass around the dividing wall and through passages of thecentrifugal bowl.

In the separation from the oil of wax in such a state apparatusembodying the principles of that shown in Sharples Patent No. 1,232,104may be effectively used.

. Moreover, I have discovered that if lubricating oil stock contains waxthat is so largely crystalline in nature that it cannot be separatedfrom the oil to a desired degree by known centrifugal processes, theaddition of amorphous wax to the oil, either by adding substantiallyoil-free petrolatum or by adding oil containing amorphous wax, causesthe resultant content of wax to be of such nature that when precipitatedby chilling it may be removed from the oil to a satisfactory degree bycentrifugal processes in order to produce oil having a suitable coldtest.

If a body of petroleum oil containing wax that is crystalline to such adegree that it may not be separated from the oil by known centrifugalprocesses is brought to a condition wherein suitable chilling, asdescribed in the above-mentioned Sharples patents and my Patent No.1,558,619, precipitates the wax in such form that the oil may be freedof wax to a suitable degree by centrifugal processes, particularly whenit is brought to such condition by addition of amorphous wax, theprecipitated wax constitutes a solid solution of crystalline wax andamorphous wax and is of greater average specific gravity thancrystalline wax and is sufficiently plastic or amorphous to pass aroundthe dividing wall and through passages of the centrifugal bowl. In orderthat the precipitate shall comprise a solid solution of crystalline waxand amorphous wax the condition of the mixture of wax and oil must beregulated, as by the addition of amorphous wax, prior to theprecipitating chilling.

If a mixture of wax and petroleum oil contains substances, other thanhard asphalt, that are commonly removed from oil or from such mixturesby acid treatment or by clay treatment or by both treatments thecentrifugal removal of wax, especially crystalline wax, and particularlythe lighter of the crystalline waxes, is thereby assisted as set forthin my copending Patent No. 1,784,525 issued December 9, 1930.Furthermore, if a mixture of wax and petroleum oil contains suchsubstances the separately discharged wax will contain a greaterpercentage of impurities than the separately discharged oil willcontain, and some impurities that are otherwise difficult to remove fromthe oil, 1. e., impurities that are most economically removed with acidor which, if removed by clay, use up the purifying qualities ofconsiderable quantity of clay, pass out of the oil in the dewaxingoperation. Another advantageous effect of the addition of amorphous waxto a mixture of wax and petroleum oil, either by adding substantiallyoil-free petrolatum or by adding oil containing amorphous wax, is thatone may thereby bring into the lubricating stock from which wax is to beremoved those substances, other than hard asphalt, that are removed byacid treatment or by clay treatment and which assist in obtainingsatisfactory removal of wax centrifugally even though the wax is in partcrystalline wax. If the mixture of petroleum oil and wax when preparedfor dilution, chilling, and

. centrifuging does not contain such substances it is advantageous thatsuch substances be added, as by the addition of any oil or oil and waxmixture containing them.

An important advantage of my invention is that by the practice thereofwax-containing petroleum oils may be centrifugally dewaxed to a suitabledegree regardless of the extent or degree to which the wax iscrystalline. Another important advantage, therefore, is that in thepractice ofmy invention it is possible centrifugally to dewax to asuitable degree petroleum oils that contain wax that is in partcrystalline but as a whole so amorphous in character that it cannot beremoved by filter pressing without preliminary cracking distillation,and petroleum oils containing wax that is in part amorphous but is as awhole so crystalline in character that it cannot be removed bypreviously known centrifugal processes. In other words, petroleum oilsthat contain wax that is too amorphous in nature to be removed to asuitable degree by filter pressing without prior cracking distillationand petroleum oils that contain wax that is too crystalline in nature tobe removed to a suitable degree by prior centrifugal processes, can bedewaxed to a suitable degree without loss in the practice of myinvention by so controlling the condition of the mixture of petroleumoil and wax that the wax, upon precipitation by chilling, is in a statein which it may be removed by centrifugal processes.

The characteristics of petroleum oils or products that contain wax thatis too amorphous in nature or character to be removed to a suitabledegree by filter-pressing without preparatory cracking distillation andis too crystalline in nature or character to be removed to a suitabledegree by prior centrifugal processes, will be further understood byageneral consideration of the variations in the characteristics of waxin different petroleum oils or products. Substantially all of the wax ina petroleum product may precipitate in crystalline form as in the caseof a cracked distillate, or alight wax-bearing fraction of petroleum,or'most distillates and some residues obtained by fire distillation; orsubstantially all of the wax may precipitate in amor-. phous form as inthe case of steam refined cylinder stock and other products abovementioned. Between these two classes which typify the limitingconditions with respect to wax content, lie petroleum products in whichboth amorphous wax and crystalline wax are precipitated together and inwhich the proportion of the total wax content that is crystalline variesfrom a large value to ,a

relatively small value and the proportion of the wax content that isamorphous varies from a small value to a relatively large value,conspicuous examples of this class of petroleum prod ucts beingwax'distilla'te and long residuum of petroleum produced by distillinggas, naphtha, burning oil and gas oil from wax-bearing petroleum. If thewax precipitated is substantially all crystalline, it may be removed byfilter-pressing but as the proportion of amorphous wax present with thecrystalline wax increases, such dewaxing becomes more and more difficultuntil the amorphous proportion attains a substantial value and thenfiltering is impracticable because of the clogging of the filter. Whenthe'wax precipitated is substantially all amorphous, it can beremoved byoperations involving separation by difference of specific gravity,including centrifugal separation, but as the proportion of crystallinewax present with the amorphous wax increases, such separating methodsbecome more and more ineffect'ive and the degree to which wax is removedwith the heavier wax by methods involving separation by difference ofspecific gravity and crystalline wax tends to clog centrifugal machines.Thus, the ratio of amorphous wax-to crystalline wax in wax theprecipitate may vary through a broad rangeand most of the petroleumproducts in which amorphous wax and crystalline wax precipitate togethercannot be dewaxed to a satistory degree by filter pressing withoutloss-incurring preliminary cracking distillation, or by methodsinvolving separation by diiferences of specific gravity and includingprior centrifugal methods.

In accordancewi-th thisinvention petroleum products consisting of amixture of oil and wax, and particularly products which could notpreviously be dewaxed to a desirable degree by methods involvingdifference of specific gravity because of the presence of crystallinewax alone or in addition to amorphous wax, are rendered dewaxable to asatisfactory degree by available methods involving difference ofspecific gravity by so controlling the condition of the mixture ofpetroleum oil and wax that the wax, upon precipitation by chilling, isin a state in which it may be removed to a satisfactory degree bymethods dependent upon difference of specific gravity, as by centrifugalseparation, the centrifugal separation herein referred to being carriedout in an imperforate bowl and the radial movement of wax particlesthrough oil or oil solution under the action of centrifugal force totheir proper zone of the bowl being termed subsidence in many instancesin this art.

Such controlling of the condition of the mixture is for the purpose ofbringing it to a condition in which wax precipitated in it, or in asolution of it in a solvent, is as a whole or in all of its parts ofsuch specific gravity and of such plasticity or amorphousness that thewax may be removed to a desired degree by available methods andapparatus depending upon separation by difference of specific gravity,leaving the oil or a solution thereof that is wax-free to a desireddegree. Such controlling of the conditicn of the mixture consists in aregulation of the amorphousness or specific gravity of the total waxpresent in the oil. Such regulation can be eifected by causing theoil-wax mixture to contain a substance or substances tending to bringthe wax to a condition in which, when precipitated it will besufficiently amorphous and will have a specific gravity suitable ornecessary to its separation from the oil by methods dependent upondifierence of specific gravity, as by centrifuging. Such substances maybe termed amorphizing substances, and they may be amorphous wax andother substances that exert desired influences on the wax present andwhich include impurities other than hard asphalt that naturally occur inpetroleum oil and are commonly removed from petroleum oil by clay oracid-treatment. Amorphizing impurities of petroleum may be caused to bepresent in the oil-wax mixture in a concentration suitable or necessaryto the removal of wax by continuous centrifugal separation, as a resultof the preparation of the oil-wax mixture, as by omitting or limitingdecolorizing treatment or by extending the distilling operation by whicha distillate oilwax mixture is produced, or by addition to the oil-waxmixture of oil or oil and wax containing such impurities as abovestated. Such amorphizing substances as amorphous wax and amorphizingimpurities of petroleum may either or both, separately or together, beadded to the oil by mixing them with the oil or by mixing with the oil asubstance containing the wax or the impurities sought to be added to theoil. Thus, in the practice of this invention one or more amorphizingsubstances is deliberately caused to be present in oil that would nototherwise be readily dewaxable by methods dependent upon difference ofspecific gravity, for the purpose of rendering the oil dewaxable by suchmethods, as contrasted with that ordinary preparation of oil fordewaxing which does not involve the premeditated bringing of suchsubstances into the oil for that purpose; and while such forming of amixture well suited to such dewaxing in accordance with this inventionmay be referred to as blending, the use of that term is not intended toimply that there is necessarily some chemical union between theingredients of the final mixture, because desired amorphizing substancescan be brought into the mixture in any convenient manner at anyappropriate stage in the preparation of the oil for the removal of waxtherefrom.

My copending application, Patent No. 1,784,525, issued December 9, 1930,is directed broadly to the ensuring of a proper concentration in the oilof such amorphizing impurities of petroleum and specifically to theaddition to the waxcontaining oil of such amorphizing impurities ofpetroleum, for the purpose of rendering dewaxable by methods dependentupon difference of specific gravity oil containing wax that is wholly orin troublesome proportion crystalline, and to the dewaxing of oilcontaining such impurities. This application is directed broadly to theregulating of the condition of crystalline-wax-containing oil to the endthat wax precipitated therein may be removed there from by methodsdependent upon difference of specific gravity, and especially bycontinuous centrifugal separation, and specifically to the ensuring of aproper concentration of amorphiz ing substances generally, andspecifically to the addition for that purpose to the oil to be dewaxedof amorphous wax alone or amorphous wax together with impurities thatnaturally occur in petroleum and are commonly removed from petroleum oilby clay or extensive acidtreatment and are other than hard asphalt.

The wax-free oil discharged from the centrifuge is heated to remove thediluent and is subjected to such purifying and fractionating operationsas may be necessary to produce the desired final products.

In petroleum oil prepared for dewaxing by centrifugal processes inaccordance with my invention, by reducing the ratio of wax ofcrystalline nature present to wax of amorphous nature present,particularly when that ratio is reduced by addition of amorphous wax,the ratio of crystalline wax to amorphous wax will depend upon thedesired nature of the wax discharged from the centrifuge, taking care,however, that the ratio is sufficiently low to ensure a removal of thewax that is sufiiciently complete to produce oil possessing the desiredcold test. Thus, if a hard wax is desired, amorphous wax of suitablequality will be added only to such' an extent that the wax removed fromthe oil will possess or can be brought to the desired degree ofhardness;

but if such proportioning of amorphous wax and crystalline wax does notbring the mixture of oil and wax to such condition that the oildischarged from the centrifuge is sufiiciently freed of wax'to give thedesired cold test then a greater proportion of amorphous wax will beadded to the oil before the chilling and centrifugal dewaxing operation.Wax removed from the oil and dischargedfrom the centrifuge is heated toremove the diluent that is added to the oil before the chilling andcentrifugal dewaxing operation. For some purposes, however, thecrystalline wax may be distilled off of the wax discharged from thecentrifuge leaving a wax residue that is substantially free ofcrystalline wax and suitable for further use in increasing the amorphouswax content of oils containing crystalline wax. The crystalline wax soobtained may be sweated or, if necessary, cracked and sweated.

I have referred above to the amorphous or crystalline nature of the waxin petroleum oils occurring or produced in different stages or types ofdistillation but consideration must also be given to the original sourceof the crude oil as different crude oils produce different mixtures ofwax and oil under the same treatment. In the practice of my invention itis also possible to gain economical advantages by securing prodnets oflower cost but containing crystalline wax and then bringing the mixtureto a condition in which the petroleum oil may be satisfactorily freed ofwax. Oil prepared for dewaxing in accordance with my invention shouldnot contain such impurities as hard asphalt but if oil and wax mixturesso prepared contain other substances above referred to the centrifugaldewaxing processes will be more effective in the removal of wax anddesirable purification will be effected as above pointed out.

To assist in the understanding of my invention I now describe threespecific advantageous applications thereof.

In common practice, in steam distillation of petroleum, naphtha andkerosene and gas oil are distilled off and then a fraction, commonlyknown as wax distillate, is distilled off, the residue being cylinderstock. or asphalt, depending upon the nature of the-crude petroleum. Infire distillation similar fractions are taken off and the wax in the waxdistillate, which distillate is sometimes called parafiin distillatewhen produced by fire distillation, is more crystalline than the wax inwax distillate produced by steam, and the residue is coke. These waxdistillates, known in practice as slop", are a mixture of oil and wax,some of the wax being crystalline and some of the wax being amorphous.Considering wax distillates as a whole, so large a proportion of the waxcontent is crystalline in nature, unless distillation has been carriedon with great care and with the use of large quantities of steam, thatthe wax distillates cannot be dewaxed by known centrifugal processes;and the wax of these distillates is so amorphous that it may not beremoved by filter pressing unless the distillates are preliminarilysubjected to cracking distillation with consequent loss of oil.

Examples of such distillates are:

A. That fraction obtained from a typical Penns lvania crude petroleum bysteam distillation which begins at seconds universal Saybolt viscosityat F. and ends when the residue has a gravity of 27'Baum or has a fire.test of 600 F.

13. That fraction obtained from a typical midcontinent crude petroleumby steam distillation which begins when the oil in the stream has aviscosity of 80 seconds universal Saybolt viscosity at 160 F. andextends to a point at which the residue is a 600 F. fire test cylinderstock.

Large quantitiesof such wax distillate, in which the wax content is tooamorphous to be removed by filter pressing and too crystalline to beremoved by centrifuging, are produced in the oil industry. Largequantities of petrolatum are also produced from all cylinder stockresidues in the production of bright stock and by centrifugaldewaxing oflong residuum of mid-continent oils.

In the practice of my invention petrolatum from these sources is addedto wax distillate in such proportion that when the mixture is dilutedand chilled the precipitated wax is in such condition that it may beremoved centrifugally from the oil and care in the production of thewax'distillate is eliminated and it is possible to dewax Wax distillateswithout preliminary injurious treatment.- While the proportions employedin preparing such a mixture must usually, because of variations due tothe source and preparatory treatment of the constituents, be determinedby experiment in accordance with the principles herein stated, I havefound that if nine parts of wax distillate (B) above-mentioned frommidcontinent-crude petroleum are mixed with one part of petrolatumobtained by cold settling, to produce bright stock, of cylinder stockthat has been acid treated to such an extent that it is green byreflected light and opaque in thick layers to transmitted light but hasnot been subjected to clay treatment, the resulting mixture may besatisfactorily dewaxed by precipitating the wax by chilling and thencentrifugally separating the wax from the oil.

In petroleum refining, oils are frequently produced that contain waxthat is definitely crystalline in nature, for example, the distillate,of cracking distillation of petroleum, wax distillate that has beensubsequently subjected to cracking distillation, and the lighterwax-containing fractions of petroleum which are sometimes kept separate.Oil containing such definitely crystalline and hard wax was formerlydewaxed by filter pressing.

In the practice of my invention amorphous wax of high melting point, forexample, wax from high fire test cylinder stock obtained from Wyomingcrude oil is added to such crystalline-wax containing oil in suchproportion that when the oil is diluted and chilled the precipitated waxcan be satisfactorily removed from the oil centrifugally. The wax soproduced is a hard wax of high melting point and is capable of immediatecommercial use. The addition of soft amorphous Wax should cause theprecipitated wax to be in such condition that it can be removed from theoil centrifugally but the final product would not be a hard wax. Whilethe proportions employed in preparing such a mixture must usually,because of variations due to the source and preparatory treatment of theconstituents, be determined by experiment in accordance with theprinciples herein stated, I have found that this operation can becarried out as follows: If the distillate producedby fire-distillationof a typical mid-continent crude petroleum is collected from the time atwhich the viscosity of the distillate stream is 50 seconds SayboltUniversal viscosity at 109 F. and

until the residues have been reduced to coke, and then burning oils andgas oils, which were produced bythe crackingthat occurred in the firstdistillation, are distilled from this distillate, the residue containscrystalline wax and is a suitable constituent for the'desired mixture.To produce a second constituent of the desired mixture a typical Wyomingcrude petroleum is distilled to remove lighter constituents and theresidue is acid treated and neutralized for the purpose of removingasphaltic impurities, and this product consisting of a topped crudepetroleum and having a green bloom is subjected to steam distillationuntil the residue has a fire test of 700 and then the residue is dilutedwith naphtha and chilled and dewaxed centrifugally, and the wax obtainedconstitutes a second constituent of the desired mixture. Fifteen partsof the wax constituent are combined with eighty-five parts of the firstconstituent to produce the desired mixture and then the mixture isdewaxed by first diluting it with 65 Baum naphtha producing a finaldiluted mixture containing 60% of naphtha and 40% of the combined firstand second constituents. The diluted mixture is heated to about 100 F.and then chilled slowly to about l0 F. and the precipitated waxseparated centrifugally. The wax-free solution of oil from thecentrifuge is steam distilled to remove the naphtha and to adjust thefinal oil to the required flash and viscosity tests. The final oil willcontain some heavy 700 F. fire test cylinder stock which was containedin the wax, either by occlusion or solid solution, that was derived fromthe Wyoming cylinder stock. The final wax fraction is steam distilled toremove naphtha and it will contain wax of high melting point derivedfrom the Wyoming cylinder stock and also hard crystalline wax derivedfrom the mid-continent distillate and this final wax may be used withoutextensive further treatment wherever a hard wax of high melting point isrequired.

Centrifugal processes dewax cylinder stocks to a high degree and producewax unusually free from oil but containing occluded oil that cannot beseparated from the wax centrifugally. It is possible to remove occludedoil by treating the Wax with naphtha and chilling and separating themixture, the wax so free from oil having a higher melting point.Petrolatum obtained from cylinder stocks by cold settling containsrelatively large quantities of oil.

In the practice of my invention petrolatum obtained from cylinder stocksand particularly that obtained by cold settling, and preferablypetroletum obtained from high fire test and high viscosity stocks, ismixed with light wax distillate, i. e., a light fraction of petroleum orof the wax distillate thereof, and the wax takes up the light oilleaving the oil free to be separated. Then the mixture is chilled andcentrifugally separated and a substantially wax-free oil of mediumviscosity is produced. As in the preparation of other mixtures hereindescribed the proportions employed in preparing this mixture mustusually, because of variations due to the source and preparatorytreatment of the constituents, be determined by experiment in accordancewith the principles herein stated, but I have found, as an example ofthis operation, that the fraction obtained by steam distillation ofmid-continent crude petroleum and lying between seconds and 150 secondsuniversal Saybolt viscosity at 100 F. may be dewaxed in accordance withmy invention if eighty-five parts of such distillate are mixed withfifteen parts of petrolatum obtained from mid-continent crude petroleumby first distilling off naphtha and burning oils and then treating withacid until the oil has lost its black color and is green by reflectedlight and then steam distilling until the residue has a fire test of 600F7 and then diluting the residue with naphtha and obtaining thepetrolatum by cold settling.

From the foregoing it will be apparent that my invention applies topetroleum oils of all kinds and to products derived therefrom, and thatthe nature of the preliminary mixing whereby the character of theprecipitated wax is controlled, is determined by the principles abovestated and with the assistance of the specific examples given. In thisconnection, the dewaxing of crude petroleum oil is entirely practicablein accordance with my invention and it results in two centrifugallyseparated fractions that are subjected to steam distillationfthe residueof one fraction being petrolatum and the residue of the other fractionbeing bright stock. And it will also be apparent that I have disclosed aprocess, and have stated the principles and have given specific examplesthereof, whereby wax may be removed by centrifugal processes to adesired degree of completeness, and to produce sufficiently wax-free oilfor any of the many uses to which petroleum oil is put, from oils inwhich the original or natural content of wax is of such nature that itcould not be removed by previously known centrifugal processes or byfilter pressing or by cold settling, it being understood that theregulation of the condition of the mixture of wax and oil is to becarried out in accordance with .my invention at any time prior to theprecipitation of the wax by chilling in the preparation for centrifugalseparation in accordance with the above-mentioned patents of Philip T.Sharples. It will also be apparent that in addition to the fact that bythe practice of this invention it is possible to dewax to a satisfactorydegree petroleum products that are necessarily produced in usualdistillery practice, but which could not previously be dewaxed withoutpreliminary cracking distillation, e. g., wax distillate formed inproducing cylinder stock, the use of my invention makes it possible toreduce greatly the amount of distillation that must be performed becausethe petroleum need not be divided or converted by distillation intoproducts containing only amorphous wax or only crystal-.

line wax. For'example, removal of only naphtha, burning oil and gas oilfrom petroleum gives aresidue, known as a long residuum, containing allof the lubricating oil of the petroleum and this may be dewaxed asdescribed herein without further distillation although it contains bothcrystalline wax and amorphous wax and could not be dewaxed byfilter-pressing or by prior methods involving difierence of specificgravity. Thus, while the proportions employed in preparing a mixture fordewaxing must usually,-

because of variations due to the source and preparatory treatment of theconstituents, be determined by experiment in accordance with theprinciples herein stated, a residue of Pennsylvania or mid-continentcrude oil, having a flash test of 350 'F. or lower, may be dewaxed inaccordance with this invention by mixing one part of petrolatum obtainedfrom clay treated cylinder stock with each ten to twenty parts of theresidue and then diluting the mixture and chilling and centrifugallyremoving the precipitated wax, the de-waxing being aided if the residuecontains its natural impurities other than hard asphalt. A reference inthe claims to oils containing crystalline wax is intended to includeboth oils that do and oils that do not contain in addition someamorphous wax.

From the foregoing it will be apparent that difliculties in centrifugalremoval of wax from oil increase as the precipitated wax is as a wholemore and more crystalline in character. Steamrefined cylinder stockssubstantially free of hard asphalt and having a flash point in excess of525 F. and a fire test in the neighborhood of 600 to 700 R, such asclay-treated residues of Appalachian oils and acidand clay-treatedresidues of certain mid-continent petroleum oils, are readily dewaxableby continuous centrifugal dewaxing, the pour test of the final productbeing proportional to the degree of chilling preparatory to centrifugalseparation of the precipitated wax. As the residue is left longer andlonger and the flash point thereof is lower and lower, the wax in theoil contains a greater and greater proportion of wax capable ofprecipitating in hard crystalline form, As the flash point of theresidue decreases through a range from 525 F. down to450 F. thedifficulties encountered in centrifugal dewaxing which are due tocrystalline wax do not ordinarily increase to such degree as to requirespecial steps for the purpose of overcoming those difficulties, but asthe flash point of the residue drops farther and farther below 450 F.the presence of crystalline wax tends more and more to cause cloggage ofthe centrifuge and to cause floating wax whichpasses out with thedewaxed oil and impairs the pour test thereof. As pointed out above thedifliculties encountered in the dewaxing of long residues because of thepresence of crystalline wax therein may be overcome by adding theretoeither petrolatum alone or oil containing markedly amorphous wax such ascylinder stock residues having a fire test as high as 600 F. or 700 F.Those difiiculties can also be overcome by the presence in the longresidue of substances other than hard asphalt which are commonly removedby clay treatment. As pointed out above, distillates of various boilingranges can be dewaxed centrifugally provided the wax precipitated by thechilling thereof is caused to be suificiently plastic and of sufiicientspecific gravity by adding to the oil to be dewaxed such amorphizingagents as either petrolatum alone or oil in which the wax is as a wholemarkedly amorphous, or by causing the oil to be dewaxed to contain suchamorphizing substances as substances other than hard asphalt which areof the nature of those commonly removed from oil by clay treatment oracid treatment. Distillates which contain sufiicient crystalline wax toimpair or prevent continuous centrifugal dewaxing thereof, and which areor can be produced in refinery practice, constitute fractions of variousboiling ranges and fiash points and comprise all or any part of the oilhaving a boiling point equal to or higher than the temperature at whichboils the lowest boiling constituent with which wax passes over. Thus,there may occur as a distillate, either as a result of batchdistillation or any type of continuous distillation, any of that part ofthe oil which distills over in batch distillation between the firstoccurrence of wax in the distillate stream and the substantiallycomplete elimination of lubricating oil constituents from the residue,leaving a residue of asphalt. In the practice of this inventiondistillates which may be dewaxed centrifugally providing there is addedthereto amorphizing substances herein identified, include distillatescomprising the whole body of oil last mentioned, distillates comprisingonly a part of that body of oil such as distillates like those abovementioned which are produced without regard to the nature of theresidue, and distillates produced in running to an asphalt residue andhaving flash tests varying from 550 F. down to 350 F. All distillates,regardless of the flash point thereof are more difficult to dewaxcentrifugally than residues of corresponding flash point, becauseof themore marked crystalline character of the wax therein. Specifically, adistillate having a flash test of 450 F. and produced by continuousdistillation, and even a so-called distillatejcylinder stock produced bycontinuous distillation and having a flash test as high as 525 F.maypresent difiicutly in the centrifugal dewaxing thereof, inasmuch asall distillates present in the continuous centrifugal dewaxing thereofmore difliculties due to crystalline wax than do residues; and suchdistillates having flash tests between 450 F. and 525 F. maybe mixed inthe proportion of 2 to 4 parts by volume with one part of a residuehaving corresponding flash point, and the resultingmixture is readilydewaxable by continuous centrifugal separation in accordance with thisinvention. This is due to the amorphizing influence of the markedlyamorphous wax in the residue upon the wax in the distillate which tendsto precipitate in crystalline form.

- What I claim as new and desire to secure by Letters Patent of theUnited States is:

1. In the dewaxing of petroleum oils containing crystalline wax, thesteps comprising by blending forming a mixture of oil with crystallinewax and amorphous wax present in such proportions that wax precipitatedfrom the 1nixture by chilling is in a state in which it is removablefrom the oil by continuous centrifugal separation, precipitating the waxby chilling, and centrifugally separating the oil and wax.

2. In the dewaxing of petroleum oils containing light crystalline wax,the steps comprising by blending forming a mixture of oil withcrystalline wax and amorphous wax present in such proportions that waxprecipitated from a naphtha solution of the mixture by chilling is ofgreater specific gravity than the residual solution, precipitating thewax by chilling such a solution, and separating the oil and wax bydiiTerence of specific gravities.

3. In the dewaxing of petroleum oils containing crystalline wax, thesteps comprising by blending forming a mixture of oil with crystallinewax and amorphous wax present in such proportions that wax precipitatedfrom a naphtha solution of the mixture by chilling is of greaterspecific gravity than the residual solution and is suflicientlyamorphous to be separated therefrom by continuous centrifugalseparation, precipitating the wax by chilling, and centrifugallyseparating the oil and wax.

4. In the dewaxing of petroleum oils containing crystalline wax, thesteps comprising by blending forming a mixture of the oil containingcrystalline wax and an amorphizing substance causing wax precipitatedfrom the mixture by chilling to possess sufficient plasticity and highenough specific gravity to be separable from the oil by continuouscentrifugal separation, precipitating the wax by chilling, andcentrifugally separating the oil and wax.

.5. In the dewaxing of petroleum oils, the steps comprising mixingtogether crystal1ine-wax-containing wax distillate of crude petroleumand petrolatum obtained from cylinder stock, in such proportions thatthe wax precipitated in the mixture by chilling is capable of beingremoved from the mixture centrifugally, precipitating the 7. In thedewaxing of petroleum oils containing crystalline wax that impairs orprevents centrifugal dewaxing of the oil, the steps comprising soregulating the condition of the mixture of oil and wax by the additionof an "amorphizing substance that the wax, upon precipitation by I.

chilling after dilution, is in a state in which it is capable of beingremoved by centrifugal separating processes, precipitating wax from theoil by chilling. and centrifugally separating the wax and oil.

8. In the dewaxing of petroleum oils containing crystalline wax thatimpairs or prevents centrifugal dewaxing of the oil, the stepscomprising adding to such oil a sufficient quantity of an amorphizingsubstance to cause all Wax precipitated from the oil by chilling to beremovable by continuous centrifugal separation, precipitating the wax bychilling, and centrifugally separating the wax and oil.

9. In the refining of wax-containing petroleum oil, the processcomprising by blending producing a mixture of oil with crystalline waxand amorphous wax of such properties and in such proportions that thewax when precipitated by chilling of the mixture is in a state in whichit may be removed from the oil by centrifugal separation and will thenbe a'hard and substantially amorphous wax of high melting point,precipitating the wax by chilling, and centrifugally separating the waxand oil.

10. In the refining of wax-containing petroleum oil, the process whichconsists in mixing with crystalline-wax-containing oil, hard amorphouswax in such proportion that precipi' tated from the mixture by chillingis capable being centrifugally separated from the oil and afterseparation possesses properties rendering it suitable for commercialuse, precipitating the wax by chilling, and centrifugaliy separating thewax and oil.

11. In the refining of wax-containing petroleum oil, the process whichcomprises mixing with crystalline-wax-containing oil, oil-containingamorphous wax in such proportions that wax precipitated from the mixtureby chilling is capable of being centrifugally separated from the oil andthe oil possesses the desired propertie precipitating the wax bychilling, and centrifugally separating the wax and oil.

12. In the refining of wax containing petroleum Oil, the process whichconsists in producing a mixture of crystalline wax-containing light oilwith amorphous wax containing occluded heavy oil, the mixture being insuch proportions that the resulting oil will have desired properties andwax precipitated therefrom by chilling will be capable of centrifugalseparation from the oil, precipitating the wax by chilling,and'centrifugally separating the wax from oil.

13. In the refining of petroleum oil, the process comprising mixing waxdistillate obtained from midcontinent crude petroleum by firedistillation and freed of lighter products of cracking with petrolatumobtained from a residue that has been neutralized and freed of asphalticimpurities and was derived from Wyoming crude petroleum, chilling theresulting mixture and thereby precipitating the wax, and centrifugallydewaxing the oil.

1%. In the dewaxing of petroleum oils, the step for rendering dewaxable,by methods involving separation of wax from oil by difference ofspecific gravity, petroleum oils containing crystalline wax that impairsor prevents dewaxing thereof by such methods, which comprises adding tosuch oil prior to the separation of wax therefrom amorphous wax andimpurities other than hard,

asphalt that are removable from petroleum oils by clay treatment.

15. In the dewaxing of petroleum oils, the step for rendering dewaxable,by methods involving separation of wax from oil by difference ofspecific gravity, petroleum oils containing crystalline wax that impairsor prevents dewaxing thereof by such method, which comprises addingamorphous wax to such oil prior to the separation of wax therefrom andwhile it contains impurities other than hard asphalt that are removablefrom petroleum oils by clay treatment.

16. In the dewaxing of petroleum oils, the step for rendering dewaxable,by methods involving separation of wax from oil by difference ofspecific gravity, petroleum oils containing crystalline Wax that impairsor prevents dewaxing thereof by such methods, which comprises addingamorphous wax to such oil prior to the separation of wax therefrom.

17. In a method for producing dewaxed mineral oil which involvesseparation of precipitated wax from oil by difference of specificgravity, the steps comprising forming a mixture of a suitable solvent, adistillate containing crystalline wax in such proportion as to impair orprevent continuous centrifugal dewaxing thereof, and a petroleum oilcontaining wax which is as a whole markedly amorphous, saidamorphous-wax-containing oil being present in such proportion that waxprecipitated from the resulting mixture by chilling is capable of beingseparated therefrom by continuous centrifugal separation; chilling theresulting mixture; and separating precipitated wax therefrom bycontinuous centrifugal separation.

18. In a method for producing dewaxed mineral oil which involvesseparation of precipitated wax from oil by difference of specificgravity, the steps comprising forming a mixture of a suitable solvent, adistillate containing crystalline wax in such proportion as to impair orprevent continuous centrifugal dewaxing thereof, and a residue which isobtained from wax-containing petroleum. and in which the wax as a wholeprecipitates in a chilled solution of the residue in a form suitable forremoval by difference of specific gravity, said residue being present insuch proportion that wax precipitated from the resulting mixture bychilling is capable of being separated from said mixture by continuouscentrifugal separation; chilling the resulting mixture; and separatingthe precipitated wax therefrom by continuous centrifugal separation.

19. In the dewaxing of mineral oil, the steps comprising forming amixture of a solvent, oil containing crystalline wax in such proportionas to impair or prevent continuous centrifugal dewaxing thereof, andadded amorphous wax, said amorphous wax being present in such proportionthat wax precipitated by reduction of temperature of the resultingmixture is sufficiently amorphous for continuous centrifugal separationfrom the solvent-oil solution; chilling the mixture and therebyprecipitating wax therein; centrifugally separating wax from the chilledmixture; separating from the separated wax the constituents thereofwhich precipitate in more crystalline form from an oil-naphtha solution,and thereby producing a residual body of wax which precipitates inamorphous form from an oil-naphtha solution; and utilizing the residualwax in the formation of additional mixture to be dewaxed.

20. In the dewaxing of mineral oil, the steps comprising forming amixture of a solvent, oil containing crystalline wax in such proportionas to impair or prevent continuous centrifugal dewaxing thereof, andadded amorphous wax, said amorphous wax being present in such proportionthat wax precipitated by reduction of temperature of the resultingmixture is sufficiently amorphous for continuous centrifugal separationfrom the solvent-oil solution; chilling the mixture and therebyprecipitating wax therein; centrifugally separating wax from the chilledmixture; distilling from the separated wax the lower boilingconstituents thereof including wax which precipitates in morecrystalline form from an oilnaphtha solution, and thereby forming aresidue of wax which precipitates in amorphous form from an oil-naphthasolution; and utilizing the residual wax in the formation of additionalmixture to be dewaxed.

21. In the dewaxing of petroleum oils, the step for rendering dewaxable,by methods involving separation of wax from oil by difference ofspecific gravity, petroleum oils containing crystalline wax that impairsor prevents dewaxing thereof by such methods, which comprises adding anamorphizing substance to such oil prior to the separation of waxtherefrom.

22. In the dewaxing of wax-containing petroleum oil, the process whichcomprises mixing with crystalline-wax-containing oil, amorphous waxcontaining impurities other than hard asphalt that are commonly removedby clay treatment or by acid treatment, said amorphous wax being Iaddedin such proportions that wax precipitated from the resulting mixture bychilling is capable of being separated from the oil by continuouscentrifugal separation, precipitating the wax by chilling, andcentrifugally separating wax and oil. 23. In the dewaxing of petroleumoils, the method of dewaxing petroleum oils containing crystalline waxthat impairs or prevents centrifugal dewaxing thereof, which comprisesadding amorphous wax to such oil prior to the removal I therefrom ofimpurities other than hard asphalt that are commonly removed byextensive acid treatment or by clay treatment, said amorphous wax beingadded in such proportions that wax precipitated from the mixture issufficiently amorlphous to be separated therefrom by continuouscentrifugal separation, precipitating the wax by chilling, andcentrifugally separating the oil and wax.

24. The method of removing slop wax from ihydrocarbon oils containingsame which consists in diluting such oil with a relatively low boilinghydrocarbon oil, adding a small quantity of petrolatum thereto,'chillingand separating the wax' from the oil. V 25. In the process of removingslop wax from iii hydrocarbon distillates containing such wax bydiluting, chilling and separating by difference in specific gravity, thesteps of adding a small quantity of petrolatum thereto before saidchilling and separation.

26. In a method for dewaxing petroleum oils involving separation ofprecipitated wax from the oil by difference of specific gravity, thesteps comprising forming a mixture comprising oil that con tains waxwhich does not settle readily when precipitated, substances naturallyoccurring in petroleum other than hard asphalt and removable therefromby clay treatment, added amorphous wax, and a suitable solvent, chillingthe resulting mixture and thereby precipitating wax therein, and thenseparating precipitated wax from the oil by difference of specificgravity.

27. A method for dewaxing a wax-containing oil involving separation ofwax from oil, which comprises adding to the oil a petroleum distillationfraction of low A. P. I. gravity containing such a substantialproportion of amorphous wax as to lend to the wax content of the waxcontaining oil the essential characteristics of amorphous Wax tocondition the wax-containing oil for removal of precipitated wax bycontinuous centrifugal separation, chilling the wax-containing oil, andthereafter removing wax from the oil.

28. A method for dewaxing a, wax-containing cil involving separation ofwax from oil, which comprises adding to the oil a petroleum residuecontaining such a substantial proportion of amorphous wax as to lend tothe wax content of the wax containing oil the essential characteristicsof amorphous wax to condition the wax-containing oil for removal ofprecipitated wax by continuous centrifugal separation, chilling thewax-containing oil, and thereafter removing wax from the oil.

29. A method for dewaxing a wax-containing oil involving separation ofwax from oil, which comprises adding to the oil a petroleum fractioncontaining such a substantial proportion of amorphous wax as to lend tothe wax content of the wax-containing oil the essential characteristicsof amorphous Wax to condition the wax-containing 3,

oil for removal of precipitated wax by continuous centrifugalseparation, chilling the wax-containingoil, and thereafter removing waxfrom the oil.

LEO D. JONES.

